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Houseplants are just outcompeted. Gall told me to look at the surface area of houseplants in your home, and then to consider the surface area of every other object in your home—the walls, the spray bottles, the couch cushions, everything. “The surface area of any vegetation is just very, very low compared with everything else that could function as a source or a sink” for air pollutants, he said.
To start to even marginally reduce indoor ozone, Gall estimated that you would need at least one houseplant for every 20 square feet of floor space. “And there are downsides to that,” he said. “You wind up having a living system in the space, and that might raise indoor humidity and cause other problems.”
Hilton Carter enjoys having a living system in his space. Carter is a filmmaker and designer whose plant-focused Instagram account has more than 163,000 followers. He told me he keeps about 185 plants in his 950-square-foot apartment in Baltimore, roughly one plant for every five square feet. “You can feel the difference in a space that’s filled with plants as opposed to a space that isn’t,” he said. “Right now, my home feels a bit more humid than it would without those plants in there.”
This humidity, while great in the winter, did somewhat limit his decoration options. “If you want to have furniture in there, it probably wouldn’t be as wise,” he said. But it’s worth it: He loves the feel of a space with plants, even if they don’t purify the air as he thought.
Yet even Carter’s apartment did not meet the strict quota for VOCs. Not even Instagram-famous plant density can cleanse a room. In fact, I found only one place that achieved one plant per square foot: Tula Plants and Design. Ries told me that the 800-square-foot store will regularly have more than 800 plants for days after a delivery. (On the day I called, it had 750.)
And Ries, as it happened, was familiar with the original Wolverton study. The store regularly shows it to customers who ask about the best air-purifying plants, she said, though employees also warn them that the study measured something very specific and was “definitely different than how it would be in our real environment.” Often, patrons walk away with peace lilies. I asked whether the newer science might change Tula’s recommendations.
“I guess I could imagine putting peace lilies all over the place. Then your home would be very full of peace lilies,” Ries said. “But unless you really loved peace lilies and snake plants, it might not be something that brings you joy.” And joy, not marginal air pollution, is the real reason to own a plant. I said that I still loved my new plants, even if they didn’t make my apartment’s air any cleaner.
“Bringing plants in, bringing greenery in—it’s about having something near you that’s alive, that you’re caring for, that brings you joy and happiness,” she said. “And that affects your mood, whether or not it’s giving you more oxygen to breathe or something.”